A 25-year-old farmer from Rajasthan presents with fever, headache, eschar (tache noire) over the ankle, and a maculopapular rash that starts on the trunk and spreads peripherally. Weil-Felix test: OX-2 titer 1:320, OX-19 positive, OX-K negative. The MOST likely diagnosis is:
- A Scrub typhus — Orientia tsutsugamushi (group: scrub typhus group)
- B Indian tick typhus — Rickettsia conorii (group: spotted fever group) ✓
- C Murine typhus — Rickettsia typhi (group: typhus group)
- D Epidemic typhus — Rickettsia prowazekii (group: typhus group)
Explanation
This is Indian tick typhus caused by Rickettsia conorii (spotted fever group Rickettsia). Key distinguishing features: eschar (tache noire) at the tick bite site, maculopapular rash starting on trunk spreading centrifugally, transmitted by Rhipicephalus sanguineus tick. Weil-Felix pattern: OX-19 and OX-2 both positive (sometimes OX-2 predominant) — this is the pattern for spotted fever group Rickettsiae. Scrub typhus (Orientia tsutsugamushi) gives OX-K positive, OX-19/OX-2 negative; R. typhi (murine typhus, louse-borne) gives OX-19 strongly positive, OX-2 weakly positive. R. prowazekii (epidemic typhus) gives high OX-19 titers. Treatment is doxycycline for all rickettsial infections.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.